Synthesis of arsenic sorbent by the reaction of magnesium hydroxide with aqueous iron(III) chloride solution

The reaction of magnesium hydroxide with a concentrated aqueous solution of iron(III) chloride yields a mixture of magnesium–iron layered double hydroxide and iron oxide–hydroxide in the akaganeite form. The content of these phases depends on the Mg/Fe atomic ratio in the starting reactant mixture. Iron oxide–hydroxide is the major reaction product at the Mg/Fe atomic ratio in the interval 1.5–1.75, and layered magnesium–iron layered double hydroxide, at Mg/Fe = 3–4. The ability of the synthesized products to take up As(III) from aqueous solutions was studied. These sorbents allow the arsenic concentration to be decreased from 3–5 mg L^–1 to values below MPC (0.01 mg L^–1).     

Biomimetic hydrocarbon oxidation catalyzed by nonheme iron(III) complexes with peracids: evidence for an Fe(V)=O species

Mononuclear nonheme iron(III) complexes of tetradentate ligands containing two deprotonated amide moieties, [Fe(Me(2)bpb)Cl(H(2)O)] (3 a) and [Fe(bpc)Cl(H(2)O)] (4 a), were prepared by substitution reactions involving the previously synthesized iron(III) complexes [Et(3)NH][Fe(Me(2)bpb)Cl(2)] (3) and [Et(3)NH][Fe(bpc)Cl(2)] (4). Complexes 3 a and 4 a were characterized by IR and elemental analysis, and complex 3 a also by X-ray crystallography. Nonheme iron(III) complexes 3, 3 a, 4, and 4 a catalyze olefin epoxidation and alcohol oxidation on treatment with m-chloroperbenzoic acid. Pairwise comparisons of the reactivity of these complexes revealed that the nature of the axial ligand (Cl(-) versus H(2)O) influences the yield of oxidation products, whereas an electronic change in the supporting chelate ligand has little effect. Hydrocarbon oxidation by these catalysts was proposed to involve an iron(V) oxo species which is formed on heterolytic O-O bond cleavage of an iron acylperoxo intermediate (FeOOC(O)R). Evidence for this iron(V) oxo species was derived from KIE (k(H)/k(D)) values, H(2) (18)O exchange experiments, and the use of peroxyphenylacetic acid (PPAA) as the peracid. Our results suggest that an Fe(V)=O moiety can form in a system wherein the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors. This work is relevant to the chemistry of mononuclear nonheme iron enzymes that are proposed to oxidize organic substrates via reaction pathways involving high-valent iron oxo species.     

Modulation of metal displacements in a saddle distorted macrocycle: synthesis, structure, and properties of high-spin Fe(III) porphyrins and implications for the hemoproteins

A rare family of five and six-coordinated high-spin Fe(III) porphyrins incorporating weak axial ligands are synthesized and structurally characterized which demonstrate, for the first time, stepwise metal displacements in a single distorted macrocyclic environment that has generally been seen in many biological systems. The introduction of four nitro groups into the meso-positions of octaethyl porphyrin severely distorts the porphyrin geometry and provides an interesting modulation of the macrocycle properties which enables the facile isolation of "pure" high-spin Fe(III)(tn-OEP)Cl, Fe(III)(tn-OEP)(MeOH)Cl, and Fe(III)(tn-OEP)(H2O)2(+) in excellent yields in a saddle distorted macrocyclic environment that are known to stabilize intermediate spin states. The stepwise out-of-plane displacements of iron are as follows: 0.47 A for Fe(III)(tn-OEP)Cl; 0.09 A for Fe(III)(tn-OEP)(MeOH)Cl, and 0.01 A for Fe(III)(tn-OEP)(H2O)2(+) from the mean plane of the porphyrins. However, in both five and six-coordinated Fe(III) porphyrins, the Fe-Np distances are quite comparable while the porphyrin cores have expanded significantly, virtually to the same extent for the six-coordinate complexes reported here. The large size of the high-spin iron(III) atom in Fe(III)(tn-OEP)(H2O)2(+) is accommodated perfectly with no displacement of the metal. This expansion is accompanied by a significant decrease of the saddle distortion with a clear increase of the ruffling. Furthermore, the Fe atom in Fe(III)(tn-OEP)(MeOH)Cl is not out of plane because of the larger atom size; however, the displacement of the iron depends on both the relative strength of the axial ligands, as well as the nature and extent of the ring deformation. Our characterization demonstrates that increase in ruffling and/or decrease in macrocycle deformation brings the iron atom more into the plane in a distorted macrocyclic environment. Our observations thus suggest that the displacements of iron in proteins are the consequences of nonequivalent axial coordination, as well as protein induced deformations at the heme. The high-spin nature of the complexes reported here is believed to be due to the larger Fe-Np distances which then reduce substantially the interaction between iron d(x2)-y2 and porphyrin a(2u) orbital. The Fe(III)/Fe(II) reduction potential of Fe(III)(tn-OEP)Cl shows a reversible peak at large positive value (0.20 V), and no ring-centered oxidation was observed within the solvent limit (approximately 1.80 V). It is thus easier to reduce Fe(III)(tn-OEP)Cl by almost 700 mV compared to Fe(III)(OEP)Cl while oxidations are very difficult. Furthermore, the addition of 3-Cl-pyridine to Fe(III)(tn-OEP)Cl in air undergoes spontaneous auto reduction to produce the rare air-stable Fe(II)(tn-OEP)(3-Cl-py)2 that shows Fe(II)/Fe(III) oxidation peaks at high positive potential (0.79 V), which is approximately 600 mV more anodic compared to [Fe(II)(tn-OEP)Cl](-). This large anodic shift illustrates the effective removal of metal-centered electron density by the macrocycle when the metal is constrained to reside in the porphyrin plane.     

Kinetics and mechanism of the iron phthalocyanine catalyzed reduction of nitrite by dithionite and sulfoxylate in aqueous solution

The reactions of sodium nitrite with sodium dithionite and sulfoxylate ion were studied in the presence of iron(III) tetrasulfophthalocyanine, Fe(III)(TSPc)3-, in aqueous alkaline solution. Kinetic parameters for the different reaction steps in the catalytic reduction by dithionite were determined. The final product of the reaction was found to be nitrous oxide. Contrary to this, the product of the catalytic reduction of nitrite by sulfoxylate was found to be ammonia. The striking difference in the reaction products is accounted for in terms of different structures of the intermediate complexes formed during the reduction by dithionite and sulfoxylate, in which nitrite is suggested to coordinate to the iron complex via nitrogen and oxygen, respectively. Sulfoxylate is shown to be a convenient reductant for the synthesis of the highly reduced iron phthalocyanine species Fe(I)(TSPc*)6- in aqueous solution. The kinetics of the reduction of Fe(I)(TSPc)5- to Fe(I)(TSPc*)6-, as well as the oxidation of the latter species by nitrite, was studied in detail.     

Origin of the unusual kinetics of iron deposition in human H-chain ferritin

From microorganisms to humans, ferritin plays a central role in the biological management of iron. The ferritins function as iron storage and detoxification proteins by oxidatively depositing iron as a hydrous ferric hydroxide mineral core within their shell-like structures. The mechanism by which the mineral core is formed has been the subject of intense investigation for many years. A diiron ferroxidase site located on the H-chain subunit of vertebrate ferritins catalyzes the oxidation of Fe(II) to Fe(III) by molecular oxygen. A previous stopped-flow kinetics study of a transient mu-peroxodiFe(III) intermediate formed at this site revealed very unusual kinetics curves, the shape of which depended markedly on the amount of iron presented to the protein. In the present work, a mathematical model for catalysis is developed that explains the observed kinetics. The model consists of two sequential mechanisms. In the first mechanism, turnover of iron at the ferroxidase site is rapid, resulting in steady-state production of the peroxo intermediate with continual formation of the mineral core until the available Fe(II) in solution is consumed. At this point, the second mechanism comes into play whereby the peroxo intermediate decays and the ferroxidase site is postulated to vacate its complement of iron. The kinetic data reveal for the first time that Fe(II) in excess of that required to saturate the ferroxidase site promotes rapid turnover of Fe(III) at this site and that the ferroxidase site plays a role in catalysis at all levels of iron loading of the protein (48-800 Fe/protein). The data also provide evidence for a second intermediate, a putative hydroperoxodiFe(III) complex, that is a decay product of the peroxo intermediate.     

Speciation of V, Cr and Fe by capillary electrophoresis-bandpass reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis-dynamic reaction cell inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the speciation of iron(III/II), vanadium(V/IV) and chromium(VI/III) is described. Two different CE migration modes were employed for separating the six metal ions using pre-capillary complexation. One is counter-electroosmotic mode in which iron(III/II) and vanadium(V/IV) ions were well separated using a 60 cm x 75 microm i.d. fused silica capillary. The voltage was set at +22 kV and a 15 mmol l(-1) tris(hydroxymethyl)aminomethane (Tris) buffer (pH 8.75) containing 0.5 mmol l(-1) ethylenediaminetetraacetic acid (EDTA) and 0.5 mmol l(-1) ortho-phenanthroline (phen) was used as the electrophoretic buffer. The other is co-electroosmotic mode in which chromium(VI/III) ions were well separated while the applied voltage was set at -22 kV and a 10 mmol l(-1) ammonium citrate buffer (pH 7.7) containing 0.5 mmol l(-1) diethylenetriaminepentaacetic acid (DTPA) and 0.01% polybrene was used as the electrophoretic buffer. The mass spectra were measured at m/z 51, 52 and 56 for V. Cr and Fe, respectively. The interfering polyatomic ions of 35Cl16O+, 40Ar12C+ and 40Ar16O+ on 51V+, 52Cr+ and 56Fe+ determination were reduced in intensity significantly by using NH3 as the reaction cell gas in the DRC. The detection limits were in the range of 0.1-0.5, 0.4-1.3 and 1.2-1.7 ng ml(-1) for V, Cr and Fe, respectively. Applications of the method for the speciation of V, Cr and Fe in wastewater were demonstrated. The recoveries were in the range of 92-120% for various species.     

Xanthene-modified and hangman iron corroles

Iron corroles modified with a xanthene scaffold are delivered from easily available starting materials in abbreviated reaction times. These new iron corroles have been spectroscopically examined with particular emphasis on defining the oxidation state of the metal center. Investigation of their electronic structure using (57)Fe Mo?ssbauer spectroscopy in conjunction with density functional theory (DFT) calculations reveals the non-innocence of the corrole ligand. Although these iron corroles contain a formal Fe(IV) center, the deprotonated corrole macrocycle ligand is one electron oxidized. The electronic ground state of these complexes is best described as an intermediate spin S = 3/2 Fe(III) site strongly antiferromagnetically coupled to the S = 1/2 of the monoradical dianion corrole [Fe(III)Cl-corrole(+?)]. We show here that iron corroles as well as xanthene-modified and hangman xanthene iron corroles are redox active and catalyze the disproportionation of hydrogen peroxide via the catalase reaction, and that this activity scales with the oxidation potential. The meso position of corrole macrocycle is susceptible toward nucleophilic attack during catalase turnover. The reactivity of peroxide within the hangman cleft reported here adds to the emerging theme that corroles are good at catalyzing two-electron activation of the oxygen-oxygen bond in a variety of substrates.     

Use of SDS micelles to stabilize a ternary intermediate in the reaction of ferrioxamine B and 1,10-phenanthroline

Spectrophotometric measurements of the reaction of ferrioxamine B (FeHDFB(+)) with 1,10-phenanthroline (phen) reveal the presence of a ternary intermediate complex in both aqueous solution and an aqueous solution of 0.16 M sodium dodecyl sulfate (SDS). The stoichiometry of the intermediate is Fe(H(2)DFB)(phen)(2+) on the basis of a Schwarzenbach analysis of spectrophotometric data obtained at variable pH and phen concentrations. The ternary complex formation constant for the reaction FeHDFB(+) + H(+) + phen right arrow over left arrow Fe(H(2)DFB)(phen)(2+) is log K = 6.96 in aqueous solution and log K = 8.64 in aqueous 0.16 M SDS. The enhanced stability of Fe(H(2)DFB)(phen)(2+) in micellar solution was analyzed in terms of the pseudophase ion-exchange (PPIE) model of micellar reactions. The association constants for the binding of each reactant to the micellar pseudophase were measured by ultrafiltration. According to PPIE model calculations, the enhanced stability of Fe(H(2)DFB)(phen)(2+) in micellar SDS arises from a proximity effect created by the high local concentrations of reactants in the micellar pseudophase. The calculations also indicate that an inhibitory medium or compartmentalization effect is operative since the observed micellar enhancement is much smaller than predicted by the PPIE model. The micellar stabilization of the Fe(H(2)DFB)(phen)(2+) intermediate and the overall conversion of FeHDFB(+) to Fe(phen)(3)(2+) are discussed as a possible model system for siderophore iron release in microbial organisms.     

Stereospecific alkane hydroxylation by non-heme iron catalysts: mechanistic evidence for an Fe(V)=O active species.

High-valent iron-oxo species have frequently been invoked in the oxidation of hydrocarbons by both heme and non-heme enzymes. Although a formally Fe(V)=O species, that is, [(Por(*))Fe(IV)=O](+), has been widely accepted as the key oxidant in stereospecific alkane hydroxylation by heme systems, it is not established that such a high-valent state can be accessed by a non-heme ligand environment. Herein we report a systematic study on alkane oxidations with H(2)O(2) catalyzed by a group of non-heme iron complexes, that is, [Fe(II)(TPA)(CH(3)CN)(2)](2+) (1, TPA = tris(2-pyridylmethyl)amine) and its alpha- and beta-substituted analogues. The reactivity patterns of this family of Fe(II)(TPA) catalysts can be modulated by the electronic and steric properties of the ligand environment, which affects the spin states of a common Fe(III)-OOH intermediate. Such an Fe(III)-peroxo species is high-spin when the TPA ligand has two or three alpha-substituents and is proposed to be directly responsible for the selective C-H bond cleavage of the alkane substrate. The thus-generated alkyl radicals, however, have relatively long lifetimes and are susceptible to radical epimerization and trapping by O(2). On the other hand, 1 and the beta-substituted Fe(II)(TPA) complexes catalyze stereospecific alkane hydroxylation by a mechanism involving both a low-spin Fe(III)-OOH intermediate and an Fe(V)=O species derived from O-O bond heterolysis. We propose that the heterolysis pathway is promoted by two factors: (a) the low-spin iron(III) center which weakens the O-O bond and (b) the binding of an adjacent water ligand that can hydrogen bond to the terminal oxygen of the hydroperoxo group and facilitate the departure of the hydroxide. Evidence for the Fe(V)=O species comes from isotope-labeling studies showing incorporation of (18)O from H(2)(18)O into the alcohol products. (18)O-incorporation occurs by H(2)(18)O binding to the low-spin Fe(III)-OOH intermediate, its conversion to a cis-H(18)O-Fe(V)=O species, and then oxo-hydroxo tautomerization. The relative contributions of the two pathways of this dual-oxidant mechanism are affected by both the electron donating ability of the TPA ligand and the strength of the C-H bond to be broken. These studies thus serve as a synthetic precedent for an Fe(V)=O species in the oxygen activation mechanisms postulated for non-heme iron enzymes such as methane monooxygenase and Rieske dioxygenases.     

Electrochemical and spectral studies on the reductive nitrosylation of water-soluble iron porphyrin

The reaction of iron(III) (meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(III)TMPyP) with nitric oxide (NO) was studied by electronic absorption spectroscopy, ESR, and electrochemical and spectroelectrochemical techniques in aqueous solutions with pH from 2.2 to 12.0. Fe(III)TMPyP has been found to undergo a reductive nitrosylation in all pHs, and the product of nitric oxide binding to the porphyrin has been determined as iron(II) porphyrin nitrosyl complex ([Fe(II)(NO)TMPyP]). The rate of the reductive nitrosylation exhibits a tendency to get faster with increase in pH. An intermediate species was observed around neutral pH by spectroelectrochemical technique and was proposed to be the iron(II) nitrosyl complex of the mu-oxo dimeric form of FeTMPyP, which is known to be a predominant in neutral solutions.     

Axial ligand and spin-state influence on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes

The present study focuses on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes formed in the [Fe(III)(tpfpp)X]/H(2)O(2)/HOO(-) system (TPFPP=5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin; X=Cl(-) or CF(3) SO(3)(-)) in acetonitrile under basic conditions at -15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high-spin [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] could be observed with the application of a low-temperature rapid-scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O-O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo- to heterolytic O-O bond cleavage is observed for high- [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron-rich porphyrin ligands, electron-deficient [Fe(III)(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe(III)(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)-oxo porphyrin π-cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.     

Differential pulse voltammetric study of the complexation of an iron porphyrin at substoichiometric levels of ligand

A new approach is presented for elucidating the complex identities of iron porphyrins when both the electrode reactant and product are strongly coordinated by an equal number of ligands. The current is monitored for each electroactive form of the complex at substoichiometric levels of ligand. The increased resolution afforded by the differential pulse technique is used to elucidate the stepwise formation of complexes. Current—voltage curves are described for perchlorato(2,3,7,8,12,13,17,18-octaethylporphinato) iron(III), in the presence of low levels of imidazole. At imidazole:porphyrin ratios of less than 2, the mono-adduct is reduced at a peak potential of —0.11 V while the bis-ligand adduct is reduced at —0.38 V. This marks the first electrochemical evidence for a mono-ligated imidazole—Fe(III) species.     

N-O bond homolysis of an iron(II) TEMPO complex yields an iron(III) oxo intermediate

The reaction of TEMPO with the iron(I) synthon PhB(MesIm)(3)Fe(COE) leads to formation of the κ(1)-TEMPO complex PhB(MesIm)(3)Fe(TEMPO). Structural and spectroscopic data establish the complex contains divalent iron bound to a nitroxido anion and is isoelectronic to an iron(II) peroxo complex. Thermolysis of the complex results in N-O bond homolysis, leading to the formation of an iron(III) oxo intermediate. The oxo intermediate is active in oxygen atom transfer reactions and can be trapped by the triphenylmethyl radical to give the iron(II) alkoxo complex PhB(MesIm)(3)Fe(OCPh(3)).     

Electrochemical Behavior of Iron(III)/Iron(II) Couple in Dimethylformamide

The electrochemical behavior of the iron(III)/iron(II) couple was investigated in both complexing (Cl⁻) and noncomplexing (ClO⁻₄) media in dimethylformamide (DMF), and the results were compared with the results obtained in aqueous solutions. The diffusion coefficients for iron(III) and iron(II) in DMF are larger in complexing medium than in noncomplexing medium, contrary to the results obtained in aqueous solutions. The heterogeneous electron transfer rate constants for the iron(III)/iron(II) couple obtained in DMF were found to be smaller in DMF solution as a result of the specific adsorption of DMF. The formal potential of the Fe(III)/Fe(II) couple in DMF is about 0.2 V less positive in noncomplexing medium as a result of the greater stabilization of iron(III) by the strongly cation-solvating DMF. The formal potential of the same couple in complexing medium (Cl⁻) was found to be 0.5 V less positive due to a combination of solvation and complexation effects. Cyclic voltammetric investigations show a quasi-reversible electron transfer without any coupled chemical reaction.     

A density functional study of O-O bond cleavage for a biomimetic non-heme iron complex demonstrating an Fe(v)-intermediate

Density functional theory using the B3LYP hybrid functional has been employed to investigate the reactivity of Fe(TPA) complexes (TPA = tris(2-pyridylmethyl)amine), which are known to catalyze stereospecific hydrocarbon oxidation when H(2)O(2) is used as oxidant. The reaction pathway leading to O-O bond heterolysis in the active catalytic species Fe(III)(TPA)-OOH has been explored, and it is shown that a high-valent iron-oxo intermediate is formed, where an Fe(V) oxidation state is attained, in agreement with previous suggestions based on experiments. In contrast to the analogous intermediate [(Por.)Fe(IV)=O](+1) in P450, the TPA ligand is not oxidized, and the electrons are extracted almost exclusively from the mononuclear iron center. The corresponding homolytic O-O bond cleavage, yielding the two oxidants Fe(IV)=O and the OH. radical, has also been considered, and it is shown that this pathway is inaccessible in the hydrocarbon oxidation reaction with Fe(TPA) and hydrogen peroxide. Investigations have also been performed for the O-O cleavage in the Fe(III)(TPA)-alkylperoxide species. In this case, the barrier for O-O homolysis is found to be slightly lower, leading to loss of stereospecificity and supporting the experimental conclusion that this is the preferred pathway for alkylperoxide oxidants. The difference between hydroperoxide and alkylperoxide as oxidant derives from the higher O-O bond strength for hydrogen peroxide (by 8.0 kcal/mol).     

Sensitive Quantification of Fe(III) in Food Samples at Screen Printed Carbon Electrode Modified with Graphene and Piroxicam by Catalytic Adsorptive Voltammetry

A new disposable sensitive voltammetric sensor for the determination of Fe(III) based on a graphene (G) and piroxicam (Pir) modified screen printed carbon electrode (Pir/G/SPCE) has been developed. The developed method is based on accumulation of Fe(III) on the surface of the prepared sensor strip, formation a complex with Pir and subsequent reduction the adsorbed chelated Fe(III) at ?0.03 V (vs. Ag/AgCl) coupled with the catalytic enhancement of bromate. Characterizations of the modified electrode surface were performed by field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS). Electrochemical behavior of the modified SPCEs was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimum conditions, the catalytic voltammetric method exhibited linear calibration plot in the concentration ranges of 1–100 ng mL^?1 and 100–3500 ng mL^?1 Fe(III) with a limit of detection of 0.3 ng mL^?1. The sensor strip displayed good reproducibility with 1.7 % relative standard deviation (RSD%). The developed method was successfully applied for the determination of iron in food samples such as vegetables, fruit, and cereal.     

Redoxkinetik von Metallkomplexen in nichtwäßrigen Lösungen,XI. Die Reduktion von Thallium(III)oxinat mit Eisen(II) in schwach koordinierenden Lösungsmitteln

The kinetics of the iron(II) reduction of thallium(III) oxinate does not differ essentially from that of the oxinate-transfer from thallium(III)-oxinate to iron(III), described before: formation of a binuclear intermediate, rearrangements within, and subsequent reaction with the excess reactant to the final products. As for the redox process, these intermediates are binuclear Tl(II)-Fe(III) complexes which, with initial reactants, form further complexes in which the second electron is transferred. In the cases of excess Tl(ox)₃ and of equimolar reactants, disproportionations are likely involved.     

In situ surface-enhanced IR absorption spectroscopy on CO adducts of iron protoporphyrin IX self-assembled on a Au electrode

The surface coordination chemistry of carbon monoxide with the reduced form (Fe(II)PP) of iron(III) protoporphyrin IX (Fe(III)PP) monolayer self-assembled on a Au electrode in 0.1 M HClO4 was studied for the first time by using in situ ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Both mono- and biscarbonyl adducts [simplified as Fe(II)(CO)PP and Fe(II)(CO)2PP, respectively] were detected, depending on the history of potential control. Initially, the Fe(II)(CO)PP predominates, and the intermediate transition potential for the conversion of Fe(II)(CO)PP to Fe(III)PP and CO was spectrally determined to be ca. 0.09 V (vs SCE). The ratio of Fe(II)(CO)2PP and Fe(II)(CO)PP increases after a potential excursion to a sufficiently positive value. Fe(II)(CO)2PP is much more stable against its electro-oxidation to Fe(III)PP than its counterpart Fe(II)(CO)PP with increasing potential. The observed change of coordination properties may be ascribed to an irreversible structural reorganization of the FePP adlayer caused by the potential excursion.     

Sorption of arsenic onto inorganic sorbents modified with iron compounds

Granulated inorganic sorbents based on silica gel of KSKG grade and aluminum oxide and modified with Fe(III) compounds were developed for water treatment to remove As(V). The influence of the particle size of the modifying additive on the ability of silica gel to take up As(V) was examined. The KSKG-based sorbents modified with nanoparticles of Fe(III) compounds exhibit the highest sorption capacity. The capacity of silica gel based sorbents modified with nanoparticles of iron compounds for As(V) is higher than that of analogous sorbents modified with iron oxides prepared by thermal decomposition of Fe(III) nitrate.     

水溶性分散型加氢催化剂催化作用的研究

以克拉玛依减压蜡油(VGO)为反应体系，对以水溶性分散型催化剂为催化体系的渣油加氢裂化过程外甩催化剂进行了分离和分析，发现单组分催化剂在反应过程中分别是以NiS（Ni7S6）、MoS2和Fe1－xS的形式存在。以二苯甲烷和克拉玛依VGO为模型化合物和反应原料，对钼、镍、铁元素单组分催化剂催化性能的研究结果表明，硫化态金属催化剂产生氢自由基中间体氢化不饱和键的“氢化活性”不同，钼催化剂明显优于镍催化剂，镍催化剂优于铁催化剂；不同催化剂抑制大分子自由基之间缩合生焦的能力也不相同，钼催化剂的抑焦能力最强，镍催化剂次之，铁催化剂的抑焦能力较差。